Feeding device and image forming apparatus

ABSTRACT

A feeding device according to the present invention holds a pile of sheets of paper in it. Feed force so acts selectively on a specified region of the upper side of the held top sheet as to feed the held sheets one after one in a feed direction. The feeding device includes a flat press plate and a support. The press plate is not smaller in the feed direction and the cross directions perpendicular to the feed direction than the maximum size of the sheets which can be held in the main body. The press plate is not larger in the feed and cross directions than the inner size of the main body. The press plate has a first opening formed over the specified region. The press plate is supported vertically movably above the held sheets by the support.

CROSS REFERENCE

This Nonprovisional application claims priority under 35 U.S.C. § 119 (a) on Patent Application No. 2007-088003 filed in Japan on Mar. 29, 2007, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

An image forming apparatus or another paper processing apparatus includes a feeding device, which includes a feed cassette. The feed cassette holds a pile of sheets of paper. The paper feeder feeds the held sheets one after one by request. In general, the paper feeder of a paper processing apparatus feeds sheets of paper in downward order from a feed cassette.

Before a feed cassette of a paper processing apparatus holds sheets of paper, they are wrapped in an airtight material so as to be low in moisture. If the apparatus is installed in a humid atmosphere, the sheets held in the feed cassette absorb moisture and may get too moist. In this case, the top sheet in the feed cassette, which is most liable to be exposed to the humid atmosphere, absorbs moisture most quickly, and the lower sheets in the cassette absorb moisture in downward order.

As the top sheet gets moist, its surface characteristics change, so that its frictional resistance decreases. This makes the top sheet liable to be misfed. This phenomenon occurs remarkably to coated paper, because SiO² or another bleaching component of the coating on the paper is more hygroscopic than cellulose or another component of the paper. Coated paper is used often for color image formation etc.

A conventional feed cassette of an image forming apparatus is fitted with a heat source for dehumidifying the sheets in the cassette in order to prevent them from being misfed by getting moist. The dehumidification by means of the heat source not only increases electric power consumption but also makes it difficult to control calorific power. If the heat source is so activated as to generate a constant amount of heat, the amount may be excessive, depending on the number or type of sheets in the feed cassette, the atmosphere in which the apparatus is installed, and which may vary, or the like. The excessive amount of heat dries the sheets, so that they may deform or discolor.

JP H05-188715 A discloses expandable and contractible covers each for covering the sheets held in a feed cassette. Each of the covers is provided to keep foreign substances from entering the associated cassette and prevent trouble during paper feeding from the cassette. There is space between each of the covers and the top sheet in the associated cassette. The space makes it impossible for some of the covers to keep the associated top sheets from being exposed to the atmosphere. Accordingly, it is impossible to reliably keep the sheets from getting moist.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a feed cassette which prevents the top sheet held in it from being exposed to the atmosphere even if the number of sheets held in the cassette changes, and which prevents the sheets from being misfed by getting moist. Another object of the invention is to provide an image forming apparatus fitted with such a feed cassette.

A feed cassette according to the present invention holds a pile of sheets of paper in it. Feed force so acts selectively on a specified region of the upper side of the held top sheet as to feed the held sheets one after one in a feed direction. The feed cassette includes a flat press plate and a support. The press plate is not smaller in the feed direction and the cross directions perpendicular to the feed direction than the maximum size of the sheets which can be held in the main body. The press plate is not larger in the feed and cross directions than the inner size of the main body. The press plate has a first opening formed over the specified region. The press plate is supported vertically movably above the held sheets by the support.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic sectional front view of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a sectional side view of a feed cassette of the apparatus.

FIG. 3 is a plan view of the press plate of the feed cassette.

FIGS. 4A and 4B are sectional side views of the feed cassette, showing how a part of the press plate shifts angularly as the number of sheets held in the cassette changes.

FIG. 5 is a plan view of the press plate of a feed cassette according to another embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

With reference to FIG. 1, an image forming apparatus 100 according to an embodiment of the present invention will be described below in detail. The apparatus 100 consists essentially of a scanner 200, an image former 300, and a paper feeder 400.

The scanner 200 includes an automatic document feeder 201, a first document platform 202, a second document platform 203, a first mirror base 204, a second mirror base 205, a lens 206, and a charge coupled device (CCD) 207.

The document feeder 201 feeds documents one after one from a document tray 211 via the second document platform 203 to an outlet tray 212. The document feeder 201 is so supported at its rear edge as to pivotably cover the upper side of the first document platform 202. A document can be placed manually on the first document platform 202 by raising the front edge of the document feeder 201 so as to expose the upper side of this platform.

The document platforms 202 and 203 are a hard glass plate. The mirror bases 204 and 205 can move horizontally under the document platforms 202 and 203. The speed at which the second mirror base 205 moves is ½ of the speed at which the first mirror base 204 moves. The first mirror base 204 carries a light source and a first mirror. The second mirror base 205 carries a second mirror and a third mirror.

The image on a document being fed over the second document platform 203 by the document feeder 201 is read with the first mirror base 204 stopping under this platform. The light source on the first mirror base 204 under the second document platform 203 radiates light to the document passing over this platform. The light reflected by the document is then reflected by the first mirror on the first mirror base 204 toward the second mirror base 205.

The image on a document placed on the first document platform 202 is read with the mirror bases 204 and 205 moving horizontally under this platform. The light source on the first mirror base 204 under the first document platform 202 radiates light to the document on this platform. The light reflected by the document is then reflected by the first mirror on the first mirror base 204 toward the second mirror base 205.

Whether the document feeder 201 is used or not, the light reflected by the document is incident on the CCD 207 via the lens 206 by means of the second and third mirrors on the second mirror base 205, with the optical path length kept constant.

The CCD 207 outputs an electric signal based on the quantity of light reflected by the document. The electric signal is input as image data into the image former 300.

The image former 300 includes a processing station 30. The processing station 30 includes a photosensitive drum 31, a charger 32, an exposure device 33, a developing device 34, a transfer belt 35, a drum cleaner 36, and a fixing device 37.

The photosensitive drum 31 has a photosensitive layer formed on its cylindrical surface and rotates clockwise in FIG. 1.

The charger 32 charges the cylindrical surface of the photosensitive drum 31 uniformly to a specified electric potential. The charger 32 may be either a non-contact type charger or a contact type charger with a roller or a brush.

The exposure device 33 irradiates the cylindrical surface of the photosensitive drum 31 with light based on the image data from the scanner 200. Photoconduction in the photosensitive layer of the drum 31 forms an electrostatic latent image on the irradiated surface of the drum 31. The exposure device 33 scans the drum surface axially of the drum 31 by means of a polygon mirror with a laser beam modulated with the image data. The exposure device 33 might be replaced by an exposure device having an array of ELs, LEDs, or other light emitting devices.

The developing device 34 supplies the cylindrical surface of the photosensitive drum 31 with toner so as to convert the electrostatic latent image into a toner image, which is visible.

The transfer belt 35 runs in a loop over rollers under the photosensitive drum 31 and has an electric resistance between about 1×10⁹ and 1×10¹³ Ω·cm.

A transfer roller 35A is supported inside the transfer belt 35 and biased to bring it into compressive contact with the cylindrical surface of the photosensitive drum 31. The transfer roller 35A corresponds to the transferrer of the present invention. A transfer voltage is applied to the transfer roller 35A, so that a transfer field is formed in a transfer zone 35B on a feed passage 11 under the drum 31.

The toner image carried by the photosensitive drum 31 is transferred to a sheet of paper passing through the nip between the drum and the transfer belt 35.

A belt cleaner 35C removes the toner, paper dust, and other dust sticking to the transfer belt 35.

The drum cleaner 36 removes the toner remaining on the portion of the drum surface from which the toner image has been transferred to the sheet passing under the photosensitive drum 31.

The processing station 30 further includes a thermister 39, which corresponds to the temperature sensor of the present invention, for sensing the temperature in the apparatus 100. The thermister 39 is positioned downstream from the fixing device 37 in the air flow created by a fan 40 in the apparatus 100. The thermister 39 can sense the temperature in the apparatus 100 which is raised by the heat radiated from the fixing device 37.

The fixing device 37 includes a heating roller 37A and a press roller 37B. The heating roller 37A is fitted with a heater lamp in it for heating it to the temperature at which the toner on a sheet of paper passing through the nip between the rollers 37A and 37B can melt. The press roller 37B is biased into compressive contact with the heating roller 37A so as to press the sheet passing through the roller nip. As a result, the toner image transferred to the sheet is fixed on it.

The paper feeder 400 includes feed cassettes 401-404 and a manual feed tray 405. Each of the feed cassettes 401-404 holds sheets of paper (record media) of a size. The feed tray 405 supports a sheet of paper of a size or quality for less frequent use.

The paper feeder 400 feeds sheets of paper one after one from one of the feed cassettes 401-404 or the manual feed tray 405. A sheet fed from the feeder 400 is then fed to the processing station 30 through the feed passage 11.

With reference to FIG. 2, the feed cassette 403 which is the feeding device of the present invention includes a main body 1, a support plate 2, a pivot plate 3, a rear end guide 4, a pair of front end guides 5, a pair of side edge guides 6, and a press plate 7.

The cassette body 1 is a hollow rectangular parallelepiped open at its top and holds a pile of sheets of paper in it. The support plate 2, pivot plate 3, end guides 4 and 5, edge guides 6, and press plate 7 are positioned in the cassette body 1.

A feed mechanism 410 feeds the sheets in the cassette body 1 one after one in downward order in a feed direction X. The feed mechanism 410 includes a pickup roller 411, a feed roller 412, a parting plate 413, and a belt 414. The feed roller 412 rotates counterclockwise in FIG. 2 and drives the belt 414, which rotates the pickup roller 411 in the same direction.

The feed mechanism 410 feeds the sheets, with the pickup roller 411 shifted downward around the feed roller 412 so that the cylindrical surface of the pickup roller 411 is in contact with a specified region of the upper side of the top sheet in the cassette body 1. The pickup roller 411 rotates with its cylindrical surface in contact with the top sheet, exerting feed force on the sheet so as to feed the sheet in the feed direction X to the nip between the feed roller 412 and parting plate 413.

If the pickup roller 411 feeds two or more sheets at a time, only the top sheet passes through the nip between the feed roller 412 and parting plate 413, while the other sheet or sheets are stopped by the friction between it or them and the plate 413.

The support plate 2 is shorter in the feed direction X than the minimum size of the sheets which can be held in the cassette body 1. The support plate 2 is supported pivotably at its rear end 2A on the bottom of the cassette body 1. Sheets of paper are held in the cassette body 1, with the bottom sheet partially lying on the support plate 2.

The pivot plate 3 is positioned under the support plate 2 and supported pivotably at its front end 3A on the bottom of the cassette body 1. The torque from a motor (not shown) biases the pivot plate 3 in a direction C around the front end 3A of this plate, so that the rear end of the pivot plate 3 shifts the support plate 2 in the opposite direction D around the rear end 2A of this plate. A spring could be used in place of the motor.

The rear end guide 4 can reciprocate in the feed direction X and the opposite direction on the bottom of the cassette body 1 and keeps in contact with the rear ends of the sheets in the body so as to regulate the positions of the sheets.

The front end guides 5 can move vertically in the cassette body 1. The heads of the front guides 5 keep in contact with the upper sides of the front corners of the top sheet in the cassette body 1. The front end guides 5 separate the top sheet from the other sheets in the cassette body 1.

The side edge guides 6 can reciprocate in cross directions Y (FIG. 3), which are perpendicular to the feed direction X, on the bottom of the cassette body 1 and keep in contact with the side edges of the sheets in the body so as to regulate the positions of the sheets.

The rear end guide 4 and side edge guides 6 can be shifted on the bottom of the cassette body 1 according to the size of the sheets in the body.

With reference to FIG. 3, the press plate 7 is substantially rectangular and flat. The press plate 7 is not smaller in the directions X and Y than the maximum size of the sheets which can be held in the cassette body 1. The press plate 7 is not larger in these directions than the inner size of the cassette body 1. The press plate 7 has a first opening 7B, a support opening 7C, a pair of second openings 7D, and a pair of third openings 7E.

The first opening 7B is formed over the specified region of the upper side of the top sheet in the cassette body 1. When the pickup roller 411 shifts downward around the feed roller 412, the pickup roller 411 passes through the first opening 7B, so that the cylindrical surface of this roller comes into contact with this region of the top sheet. With the roller surface in contact with the top sheet, the rotation of the pickup roller 411 exerts feed force on the sheet.

The rear end guide 4 passes vertically through the support opening 7C, which restricts the forward and backward movements of the press plate 7 while this plate is moving vertically in the cassette body 1. The top of the rear end guide 4 is exposed, so that this guide is easy to pull out through the support opening 7C. Accordingly, the press plate 7 can be removed upward from the rear end guide 4. The rear end guide 4 functions as the support of the present invention.

Alternatively, the cassette body 1 might be fitted with a support on one side of it, with which part of the press plate 7 would engage vertically movably. In this case, the rear end guide 4 would not function as the support.

Each of the front end guides 5 can move vertically through one of the second openings 7D. Each of the side edge guides 6 passes vertically through one of the third openings 7E.

With the press plate 7 removed from the cassette body 1, sheets of paper are put into the body. Subsequently, the press plate 7 is placed on the top sheet in the cassette body 1, with the support opening 7C engaging with the rear end guide 4. This enables the press plate 7 to move vertically. Without external force exerted on the press plate 7, the weight of this plate makes it rest on the top sheet.

The press plate 7 covers the top sheet in the cassette body 1 except where the sheet is exposed through the openings 7B-7E. As a result, the substantially whole area of the top sheet is not exposed to the atmosphere. This keeps the top sheet from getting so moist in a humid atmosphere that the pickup roller 411 might slip on the sheet and misfeed it.

As the number of sheets in the cassette body 1 decreases, the support plate 2 shifts in the direction D (FIG. 2), so that front portions of the sheets tilt in this direction. If the press plate 7 kept flat, it could not keep in close contact with the upper side of the top sheet in the cassette body 1.

The press plate 7 includes a flexing portion 7A extending across it in the cross directions Y. The flexing portion 7A divides the press plate 7 into a front part and a rear part, the angle between which can vary. Even when the inclination of front portions of the sheets in the cassette body 1 varies, as shown in FIGS. 4A and 4B, the press plate 7 keeps in close contact with a wide area of the top sheet in the body.

The flexing portion 7A may be made of a flexible material of a specified length in the direction X. An elastic member may be stuck to the under side of the press plate 7 so that this plate can more reliably cover the top sheet in the cassette body 1.

The press plate 7 may be made of a transparent material. This makes it possible to observe the type and states of the sheets in the cassette body 1 visually without removing the press plate 7.

FIG. 5 shows the press plate 71 of a feed cassette according to another embodiment of the present invention. The press plate 71 has a front cutout 71B and a pair of side cutouts 71E, which correspond to the first opening 7B and third openings 7E respectively of the press plate 7.

The two embodiments have been described with an image forming apparatus exemplifying a paper processing apparatus. However, the present invention can be applied likewise to other paper processing apparatus than image forming apparatus which holds a pile of sheets of paper.

The present invention being thus described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. 

1. A feeding device comprising: a main body for holding a pile of sheets of paper therein; wherein feed force so acts selectively on a specified region of the upper side of the held top sheet as to feed the held sheets one after one in a feed direction; a press plate being shaped like a flat plate being in length in the feed direction and the cross directions perpendicular to the feed direction, not smaller than the maximum size of sheets capable of being held in the main body and not larger than the inner size of the main body; the press plate having a first opening formed over the specified region; and a support so supporting the press plate above the held sheets that the press plate can move vertically.
 2. A feeding device as claimed in claim 1, wherein the press plate can be removed upward from the support.
 3. A feeding device as claimed in claim 1, wherein the support is a rear end guide limiting the upstream movement of the held sheets in the feed direction.
 4. A feeding device as claimed in claim 1, further comprising: a front end guide for contact with a front corner of the upper side of the held top sheet on the downstream side in the feed direction; the press plate having a second opening through which the front end guide passes vertically.
 5. A feeding device as claimed in claim 1, further comprising: a side edge guide for contact with side edges of the held sheets parallel in the feed direction; the press plate having a third opening through which the side edge guide passes vertically.
 6. A feeding device as claimed in claim 1, wherein the press plate includes a flexing portion extending thereacross in the cross directions, in the middle part of the press plate in the feed direction.
 7. A feeding device as claimed in claim 1, wherein the press plate is made of a transparent material.
 8. An image forming apparatus comprising an image former for forming an image on a sheet of paper fed from a feeding device as claimed in claim
 1. 